2010 Section B Question 2 (Testing)

Question 1

Outline two reasons for the mechanical testing of metals to the point of destruction.

Answer 1

Its a method of quality control

determines the success of heat treatment on products

gives specific data about things such as strength, ductility, toughness etc…

gives information about suitability of material before used in product

Question 2

Describe the main features of the Izod impact test with reference to:

the purpose of the test
principle of operation

Answer 2

Has a striking energy of 167 joules and is held vertically

Test pieces are notched and held in the vice associated with the machine.

Pendelum strikes the test piece and determines the energy absorbed in breaking the piece

This gives a numerical value for the toughness of the material

Question 3

Describe Eddy current testing

Answer 3

Eddy current tests are most effective for testing non-ferrous
metals of uniform section.

A coil, energised with high frequency alternating current, is
placed close to a conductive material producing eddy
currents on the material.

A magnetic field is produced in
the test specimen by the currents.

A defect will distort this
magnetic field

The defect will be located by the coil and recorded electronically

Question 4

Describe radiography (X-ray) testing

Answer 4

Radiation from an x-ray tube is passed through
the weld.

If no defects are present, the amount of
absorption is uniform across the area exposed to
the x-ray beam.

If a defect is present in the weld,
a smaller amount of rays is absorbed

This can be detected by placing a photographic
film on the side of the material opposite the
radiation source.

On a negative film, the defect
shows as a dark spot.